Why Key pairs for SSH access in AWS? - Purpose & Use Cases

The Big Idea

Discover how a simple pair of keys can lock down your cloud server better than any password.

The Scenario

Imagine you want to connect to your cloud server by typing a password every time. You write down passwords on paper or share them by email with your team.

The Problem

This is slow and risky. Passwords can be guessed, stolen, or lost. Sharing passwords means anyone can access your server, causing security problems and confusion.

The Solution

Key pairs use two linked keys: one public and one private. The public key goes to the server, and the private key stays with you. This lets you connect securely without typing passwords, and only you can access the server.

Before vs After

✗ Before

ssh user@server-ip
# then type password

✓ After

ssh -i my-key.pem user@server-ip

What It Enables

It makes secure, fast, and password-free access to your cloud servers possible.

Real Life Example

A developer can safely connect to a cloud server from anywhere without risking password leaks or delays.

Key Takeaways

Manual password access is slow and unsafe.

Key pairs use public and private keys for secure login.

This method protects your server and speeds up access.

Practice

1. What is the main purpose of a key pair in AWS for SSH access?

easy

A. To store server data securely

B. To securely connect to a server without using a password

C. To create a backup of the server

D. To monitor server performance

Solution

1. Step 1: Understand SSH access

   SSH uses keys to allow secure login without passwords.

2. Step 2: Role of key pairs in AWS

   A key pair provides a private key for the user and a public key for the server to verify identity.

3. Final Answer:

   To securely connect to a server without using a password -> Option B

4. Quick Check:

   Key pairs enable passwordless secure login [OK]

Hint: Key pairs replace passwords for secure server login [OK]

Common Mistakes:

• Thinking key pairs store server data
• Confusing key pairs with backups
• Assuming key pairs monitor performance

2. Which AWS CLI command correctly creates a new key pair named MyKey and saves the private key to a file?

easy

A. aws ec2 create-key-pair --key-name MyKey --query 'KeyMaterial' --output text > MyKey.pem

B. aws ec2 create-key-pair MyKey > MyKey.pem

C. aws ec2 generate-key-pair --name MyKey > MyKey.pem

D. aws ec2 new-key --key-name MyKey > MyKey.pem

Solution

1. Step 1: Identify correct AWS CLI syntax

   The correct command uses create-key-pair with --key-name and outputs the private key material.

2. Step 2: Confirm output redirection

   The private key is saved by redirecting the output to a file with > MyKey.pem.

3. Final Answer:

   aws ec2 create-key-pair --key-name MyKey --query 'KeyMaterial' --output text > MyKey.pem -> Option A

4. Quick Check:

   Correct AWS CLI syntax for key pair creation [OK]

Hint: Use create-key-pair with --query 'KeyMaterial' to save private key [OK]

Common Mistakes:

• Using wrong command like generate-key-pair
• Omitting --query to extract key material
• Not redirecting output to save private key

3. You launched an EC2 instance with key pair MyKey. Which command will you use to connect to it if the instance's public IP is 54.12.34.56 and your private key file is MyKey.pem?

medium

A. ssh ec2-user@54.12.34.56 -i MyKey.pem

B. ssh -key MyKey.pem ec2-user@54.12.34.56

C. ssh -p MyKey.pem ec2-user@54.12.34.56

D. ssh -i MyKey.pem ec2-user@54.12.34.56

Solution

1. Step 1: Understand SSH command syntax for key usage

   The -i option specifies the private key file for authentication.

2. Step 2: Confirm correct order of arguments

   The correct syntax is ssh -i private_key user@host. ssh -i MyKey.pem ec2-user@54.12.34.56 matches this exactly.

3. Final Answer:

   ssh -i MyKey.pem ec2-user@54.12.34.56 -> Option D

4. Quick Check:

   SSH uses -i to specify private key file [OK]

Hint: Use ssh -i private_key user@ip to connect [OK]

Common Mistakes:

• Using -key or -p instead of -i
• Placing -i after user@host
• Omitting the private key option

4. You tried to connect to your EC2 instance using SSH but got a permission denied error. Which of these is the most likely cause?

medium

A. The private key file has incorrect permissions (too open)

B. The instance is stopped

C. The key pair was deleted from AWS

D. The instance has no public IP

Solution

1. Step 1: Check SSH private key file permissions

   SSH requires private key files to have strict permissions (e.g., 400). Too open permissions cause denial.

2. Step 2: Understand other options

   While stopped instances or no public IP prevent connection, the error message differs. Deleted key pairs do not affect existing instances.

3. Final Answer:

   The private key file has incorrect permissions (too open) -> Option A

4. Quick Check:

   Private key file permissions cause SSH denial [OK]

Hint: Set private key file permission to 400 or stricter [OK]

Common Mistakes:

• Ignoring file permission errors
• Assuming instance state causes permission denied
• Confusing deleted key pairs with connection errors

5. You lost your private key file for an EC2 instance launched with key pair OldKey. What is the best way to regain SSH access without stopping the instance?

hard

A. Use the AWS console to download the lost private key again

B. Delete the instance and launch a new one with a new key pair

C. Create a new key pair, then update the instance's authorized keys by connecting through Systems Manager or another user

D. Generate a new private key file with the same key name in AWS

Solution

1. Step 1: Understand private key loss impact

   Private keys cannot be recovered or downloaded again from AWS once lost.

2. Step 2: Regain access without stopping instance

   Use AWS Systems Manager or another user with access to add a new public key from a new key pair to the instance's authorized keys.

3. Final Answer:

   Create a new key pair, then update the instance's authorized keys by connecting through Systems Manager or another user -> Option C

4. Quick Check:

   Lost private key requires new key and authorized keys update [OK]

Hint: Use Systems Manager to add new key without stopping instance [OK]

Common Mistakes:

• Trying to download lost private key again
• Assuming new key pair with same name works
• Deleting instance unnecessarily